This Patent Application claims priority of Japanese Patent Applications: No. 2000-306042, filed: Oct. 5, 2000; No. 2000-328193, filed: Oct. 27, 2000; No. 2001-41444, filed: Feb. 19, 2001; No. 2001-099029, filed: Mar. 30, 2001; and No. 2001-137180, filed: May 8, 2001.
The present invention relates to a SHEET FOR INK JET-RECORDING for use in forming recorded images using liquid ink such as water-based ink and, in particular, to a sheet for ink jet-recording (an INK JET-RECORDING SHEET), which never undergoes any color change during or after long-term storage, which is a disadvantage observed for the conventional ink jet-recording sheet, while maintaining such advantages that it can ensure a high density of full color-printed images formed thereon and that it is excellent in ink absorptivity.
The ink jet-recording system, in which images are formed by injecting water-based ink on a recording medium through a fine nozzle, has widely been used in, for instance, printers for terminal devices, facsimiles, plotters or devices for printing account books and slips. This is because, for instance, it has a low noise level during recording operations; it easily permits the color printing; it also permits high-speed recording; and it is less expensive as compared with other printing devices.
On the other hand, printers have rapidly been popularized recently and they have increasingly been required to give finer and more precise images at a high speed. In addition, there has recently been developed a digital camera. Correspondingly, recording mediums have been required to have higher recording characteristic properties. More specifically, there has been desired for the development of a recording medium, which is not only excellent in ink absorptivity, recording density, water resistance and storability, but also has image quality and shelf life almost comparable to those observed for the images formed on the silver halide system.
To satisfy such requirements, there have been proposed a large number of sheets each comprising a substrate provided thereon with an ink-receiving layer, which mainly comprises a pigment and a binder. For instance, there have been reported a variety of methods for applying, onto substrates, a coating layer comprising amorphous silica and a polymer binder (Japanese Un-Examined Patent Publication (hereunder referred to as xe2x80x9cJ. P. KOKAIxe2x80x9d No. Sho 55-51583, J. P. KOKAI No. Sho 57-157786 and J. P. KOKAI No. Sho 62-158084); a coating layer comprising an ink-adsorbing pigment such as zeolite (J. P. KOKAI No. Sho 56-144172); a coating layer comprising finely pulverized silicic acid and a water-soluble resin (J. P. KOKAI No. Sho 56-148583); and a coating layer comprising a porous and cationic alumina hydrate (J. P. KOKAI No. Sho 60-232990).
Moreover, there have also been proposed methods, which comprise incorporating, for instance, cationic polymers (J. P. KOKAI No. Sho 56-84992, J. P. KOKAI No. Sho 60-49990 and J. P. KOKAI No. Sho 61-125878); and basic latexes (J. P. KOKAI No. Sho 57-36692) into the ink-receiving layers, in order to improve the water resistance of printed letters.
Furthermore, there have also been proposed, for instance, methods, which comprise adding, to the ink-receiving layer, at least one member selected from the group consisting of metal oxides and metal chlorides such as phosphorus tungstate, phosphorus molybdate and chromic chloride, and tannic acid (J. P. KOKAI No. Sho 57-87987); an antioxidant such as a hindered phenol (J. P. KOKAI No. Sho 57-74192); hindered amines (J. P. KOKAI No. Sho 61-146591); UV light absorbers such as benzophenone type, benzotriazole type and phenyl salicylic acid type ones (J. P. KOKAI No. Sho 57-74193, J. P. KOKAI No. Sho 57-87988 and J. P. KOKAI No. Sho 63-222885); a thiourea type compound (J. P. KOKAI No. Sho 61-163886); a specific mercapto compound such as 2-mercaptobenzothiazole and 2-mercaptobenzimidazole (J. P. KOKAI No. Sho 61-177279); and a dithiocarbamic acid salt, a thiuram salt, a thiocyanic acid ester or a thiocyanic acid salt (J. P. KOKAI No. Hei 7-314882).
However, the full color ink jet recorded images formed according to these techniques suffer from a problem of color change during a long-term storage and in particular, when a phthalocyanine dye is used as the dye for cyan color ink, these techniques have still been insufficient since the images cause color change along with the discoloration of the phthalocyanine dye.
Accordingly, it is an object of the present invention to provide an ink jet-recording sheet, which does not suffer from the drawbacks associated with the conventional ink jet-recording sheet, and more specifically to an ink jet-recording sheet, which never undergoes any color change during or after a long-term storage even when the sheet is subjected to full color printing operations and which permits the considerable reduction of such color change, particularly observed when a phthalocyanine dye is used as the dye for cyan color ink, along with the discoloration of the phthalocyanine dye.
The inventors of this invention have conducted various studies of an ink jet-recording sheet for forming recorded images using liquid ink such as water-based ink, have found that when incorporating, into the recording sheet, a specific compound including a sulfur atom in the molecule and a polymer of a diallylamine type compound, an ink jet-recording sheet free of any drawback associated with the conventional ink jet-recording sheet can be obtained and more specifically, the resulting ink jet-recording sheet never undergoes any color change during or after a long-term storage even when the sheet is subjected to full color printing operations and the sheet permits the considerable reduction of such color change, particularly observed when a phthalocyanine dye is used as the dye for cyan color ink, along with the discoloration of the phthalocyanine dye, and thus have completed the present invention.
According to the present invention, there is thus provided an ink jet-recording sheet for forming recorded images using liquid ink, wherein the sheet comprises (a) at least one member selected from the group consisting of those represented by the following general formulae (1) to (5) and salts of compounds represented by the following general formulae (3) and (4); and (b) at least one member selected from the group consisting of homopolymers of diallylamine compounds represented by the following general formula (6) and copolymers of the compounds of formula (6) with copolymerizable ethylenically unsaturated compounds.
HOxe2x80x94(C2H4(S)r)pxe2x80x94R1xe2x80x83xe2x80x83(1) 
R2xe2x80x94(S)txe2x80x94(CH2)qxe2x80x94(S)txe2x80x94R3xe2x80x83xe2x80x83(2) 
HOOCxe2x80x94(CH2)1xe2x80x94(S)nxe2x80x94(CH2)mxe2x80x94COOHxe2x80x83xe2x80x83(3) 
wherein R1, R2 and R3 each represents a C1 to C4 alkyl group, a C1 to C4 hydroxyalkyl group or a C1 to C4 dihydroxyalkyl group; R4 and R5 each represent a hydrogen atom or a C1 to C4 alkyl group; R6 to R9 each represents a hydrogen atom, a C1 to C4 alkyl group, a C1 to C4 alkylcarbonyl group or a benzoyl group; R10 and R11 each represents a C1 to C4 alkyl group or a C1 to C4 alkoxy group; R12 and R13 each represents a hydrogen atom or a methyl group; R14 represents a hydrogen atom or a C1 to C4 alkyl group; and HX represents an acid, and p represents an integer ranging from 1 to 3; q represents an integer ranging from 1 to 6; r, t, n and u each represents 1 or 2; 1 and m each represents an integer ranging from 1 to 11; w represents an integer ranging from 1 to 6; y and z each represents 0 or an integer ranging from 1 to 3.
The present invention will now be described in more detail with reference to the following preferred embodiments.
Specific examples of the compounds represented by formulas (1) and (2) include 2,2xe2x80x2-thiodiethanol, 2,2xe2x80x2-dithiodiethanol, 1,2-bis (2-hydroxyethylthio) ethane, 1,2-bis (2-hydroxyethyldithio) ethane, 2,2xe2x80x2-bis (2-hydroxyethylthio) diethyl sulfide, 2,2xe2x80x2-bis (2-hydroxyethylthio) diethyl disulfide, bis (2-hydroxyethylthio) methane, bis (2-hydroxyethyldithio) methane, 1,3-bis (2-hydroxyethylthio) propane, 1,3-bis (2-hydroxyethyl-dithio) propane, 1,4-bis (2-hydroxyethylthio) butane, 1,4-bis (2-hydroxyethyldithio) butane, 1,6-bis (2-hydroxyethylthio) hexane, 1,6-bis (2-hydroxyethyldithio) hexane, ethylthioethanol, ethyldithioethanol, n-propylthioethanol, isopropylthioethanol, isopropyldithioethanol, n-butylthioethanol, 1-ethylthio-1-(2-hydroxyethylthio) methane, 1-ethylthio-2-(2-hydroxyethylthio) ethane, 1-ethylthio-3-(2-hydroxyethylthio) propane, 1-ethylthio-4-(2-hydroxyethylthio) butane, 1,1-bis (2,3-dihydroxypropylthio) methane, 1,2-bis (2,3-dihydroxypropylthio) ethane, 1,3-bis (2,3-dihydroxypropyldithio) propane, 1,4-bis (2,3-dihydroxypropylthio) butane, 1,6-bis (2,3-dihydroxypropylthio) hexane and 1-ethylthio-2-(2,3-dihydroxy-propylthio) ethane.
Among these compounds, particularly preferably used herein are 1,2-bis (2-hydroxyethylthio) ethane and 1,4-bis (2-hydroxyethylthio) butane because of their high color change-inhibitory effect and high safety.
Specific examples of the compounds represented by formula (3) are 2,2xe2x80x2-thiodiglycolic acid, 3,3xe2x80x2-thiodipropionic acid, 4,4xe2x80x2-thiodibutanoic acid, 6,6xe2x80x2-thiodicaproic acid, 8, 8xe2x80x2-thiodicaprylic acid, 10,10xe2x80x2-thiodicapric acid, 12,12xe2x80x2-thiodilauric acid, 2,2xe2x80x2-dithiodiglycolic acid, 3,3xe2x80x2-dithiodipropionic acid, 4,4xe2x80x2-dithiodibutanoic acid, 6,6xe2x80x2-dithiodicaproic acid, 8,8xe2x80x2-dithiodicaprylic acid, 10,10xe2x80x2-dithiodicapric acid and 12,12xe2x80x2-dithiodilauric acid.
Among these compounds, particularly preferably used herein are 3,3xe2x80x2-thiodipropionic acid and 3,3xe2x80x2-dithiodipropionic acid because of their high color changexe2x80x94inhibitory effect and high safety.
Specific examples of the compounds represented by the general formula (4) are 3,3xe2x80x2-dithiobis (2-aminopropionic acid), 3,3xe2x80x2-thiobis (2-aminopropionic acid), dimethyl 3,3xe2x80x2-dithiobis (2-aminopropionate), dimethyl 3,3xe2x80x2-thiobis (2-aminopropionate), diethyl 3,3xe2x80x2-dithiobis (2-aminopropionate), diethyl 3,3xe2x80x2-thiobis (2-aminopropionate), diisopropyl 3,3xe2x80x2-dithiobis (2-aminopropionate), di n-butyl 3,3xe2x80x2-dithiobis (2-aminopropionate), 3,3xe2x80x2-dithiobis (2-N-acetyl aminopropionic acid), 3,3xe2x80x2-thiobis (2-N-acetylaminopropionic acid), dimethyl 3,3xe2x80x2-dithiobis (2-N-acetylaminopropionate), dimethyl 3,3xe2x80x2-thiobis (2-N-acetyl aminopropionate), dimethyl 3,3xe2x80x2-dithiobis (2-N-benzoyl aminopropionate) and dimethyl 3,3xe2x80x2-thiobis (2-N-benzoyl aminopropionate).
Particularly preferably used herein is 3,3xe2x80x2-dithiobis (2-aminopropionic acid) among others, because of its high color change-inhibitory effect and high safety.
Specific examples of the compounds represented by the foregoing general formula (5) are 1,2-bis (phenylthio) ethane, 1,3-bis (phenylthio) propane, 1,4-bis (phenylthio) butane, 1,5-bis (phenylthio) pentane, 1,6-bis (phenylthio) hexane, 1,2-bis (4-methylphenylthio) ethane, 1,4-bis (4-methylphenylthio) butane, 1,6-bis (4-methylphenylthio) hexane, 1-phenylthio-2-(4-methylphenylthio) ethane, 1-phenylthio-4-(4-methylphenylthio) butane, 1-phenylthio-6-(4-methylphenylthio) hexane, 1,4-bis (2-methylphenylthio) butane, 1,4-bis (3-methylphenylthio) butane, 1,4-bis (3,4-dimethylphenylthio) butane, 1,4-bis (2,3,4-trimethylphenylthio) butane, 1,4-bis (4-ethylphenylthio) butane, 1,4-bis (4-t-butylphenylthio) butane, 1,2-bis (4-methoxyphenylthio) ethane, 1,4-bis (4-methoxyphenylthio) butane, 1,6-bis (4-methoxyphenylthio) hexane, 1,4-bis (4-isopropoxyphenylthio) butane, 1-phenylthio-4-(4-methoxyphenylthio) butane and 1-phenylthio-4-(4-isopropoxyphenylthio) butane.
In this respect, particularly preferably used herein are 1, 4-bis (phenylthio) butane and 1,6-bis (phenylthio) hexane among others, because of their high color change-inhibitory effect.
Examples of ions as the counterparts of the salts of the compounds represented by the general formula (3) or (4) include sodium, potassium, magnesium, calcium, ammonium and zinc.
The acid represented by the foregoing general formula HX of (6) may be either inorganic or organic ones and specific examples thereof include inorganic acids such as hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, pyrophosphoric acid and metaphosphoric acid; and organic acids such as formic acid, acetic acid, propionic acid, methanesulfonic acid and p-toluenesulfonic acid. Among these acids, particularly preferably used herein are hydrochloric acid and sulfuric acid, because of their high color change-inhibitory effect. In the foregoing formulas, R12, R13 and R14 preferably represent a hydrogen atom.
Examples of the homopolymers and copolymers of the diallylamine compounds represented by the general formula (6) are poly (diallylamine) hydrochloride, poly (diallylamine) sulfate, poly (diallylamine) phosphate, poly (diallylamine) acetate, poly (diallylamine) propionate, poly (diallylamine) methanesulfonate, poly (diallylmethylamine) hydrochloride, poly (diallylmethylamine) sulfate, poly (diallylethylamine) hydrochloride, poly (diallylethylamine) sulfate, poly (diallyl-n-propylamine) hydrochloride, poly(diallyl-n-butylamine) hydrochloride, poly (di-2-methylallylamine)hydrochloride, poly (di-2-methylallylamine) sulfate, diallylamine hydrochloride-acrylamide copolymer, diallylamine sulfate-acrylamide copolymer, diallylamine phosphate-acrylamide copolymer, diallylmethylamine hydrochloride-acrylamide copolymer, diallylmethylamine sulfate-acrylamide copolymer, diallylmethylamine phosphate-acrylamide copolymer, diallylethylamine hydrochloride-acrylamide copolymer, diallylamine hydrochloride-sulfur dioxide copolymer, diallylamine sulfate-sulfur dioxide copolymer, diallylmethylamine hydrochloride-sulfur dioxide copolymer and diallylethylamine hydrochloride-sulfur dioxide copolymer. Among these polymers and copolymers, preferably used herein are those having a molecular weight ranging from 10,000 to 200,000.
These polymers and copolymers ensure the achievement of the synergistic effects of improving water resistance and color change-inhibition.
As has been discussed above, full color ink jet-recorded images undergo color change during a long-term storage and, in particular, when a phthalocyanine dye is used as the dye for cyan color ink, a significant color change is observed along with the discoloration of the dye. It would be recognized that this color change is caused due to the easy and preferential oxidation of the cyan dye carrying a phthalocyanine skeleton by gases present in the air, in particular, those having a strong oxidative effect such as ozone.
Although the reason why the compounds represented by the general formulas (1) to (5) and salts of the compounds of formulas (3) and (4) are particularly effective in the inhibition of any color change of the ink jet-recording sheet has not yet been clearly elucidated, it would be recognized that the compounds of formulas (1) to (5) and the salts of the compounds of formulas (3) and (4) are quite susceptible to a gas having a strong oxidative effect such as ozone, that they are accordingly oxidized prior to the oxidation of the cyan dye and therefore, the cyan dye is protected from any oxidation.
Moreover, the compounds formed through the oxidation of the compounds of formulas (1) to (5) and salts of formulas (3) and (4) are colorless and therefore, it is important characteristic properties of the ink jet-recording sheet of the present invention that it does not suffer from a problem of, for instance, any yellowing of the sheet thereof.
The content of the compounds represented by the foregoing formulas (1) to (5) and salts of formulas (3) and (4) in the ink jet-recording sheet is on the order of about 0.1 to 4 g/m2 and preferably 0.2 to 2 g/m2. This is because if the content thereof is less than 0.1 g/m2, the intended effect of improving the shelf life of the recorded images may be insufficient, while if it exceeds 4 g/m2, the quality of the resulting images may be impaired.
The content of the homopolymers and copolymer of the compound represented by formula (6) in the ink jet-recording sheet in general ranges from 1 to 100 parts by weight and preferably 5 to 50 parts by weight per 100 parts by weight of the pigment. This is because if the content thereof is less than the lower limit, the resulting sheet may be insufficient in the effect of improving the shelf life and it is difficult to obtain the desired effects of improving, for instance, the water resistance and density of printed letters. On the other hand, if the content exceeds the upper limit, the density of printed letters may be reduced and images may cause bleeding.
As methods for preparing an ink jet-recording sheet comprising the compound represented by the foregoing formulas (1) to (5) and salts of formulas (3) and (4) and the homopolymers or copolymer of the compound of the general formula (6), there may be listed, for instance, a method in which base paper is coated or impregnated with a coating liquid containing specific compounds using a size press, for instance, during paper-making process; a method which comprises the steps of applying a coating liquid for forming an ink-receiving layer prepared by mixing an ink absorptive pigment, an adhesive and specific compounds onto a substrate such as paper (acidic paper, neutral paper), synthetic paper, a plastic film or a non-woven fabric using a coating machine and then drying the coated layer to give an ink-receiving layer; and a method which comprises the step of applying a coating liquid containing specific compounds onto the surface of an ink-receiving layer comprising a pigment, an adhesive and a specific polymer.
Among these methods, preferably used herein is the method in which the foregoing specific compounds are incorporated into the ink-receiving layer since the method is highly effective in inhibiting any color change of images.
If the compounds of the foregoing formulas (1) to (5) and the salts of the compounds of formulas (3) and (4) are soluble in water, an aqueous solution thereof is incorporated into a coating liquid for forming an ink-receiving layer or applied onto an ink-receiving layer. On the other hand, if they are less soluble in water, they are finely pulverized in an agitation-pulverization machine such as a ball mill, an attritor, a sand mill or a colloid mill, while using water as a dispersion medium.
Examples of substrates for ink jet-recording sheets usable herein are paper (acidic paper, neutral paper), synthetic paper, a plastic film, a non-woven fabric, a plastic film laminated with coated paper or wood-free paper through an adhesive layer or a laminate of paper with a plastic film. Examples of such plastic films are polyester, polypropylene and nylon films.
Examples of pigments to be incorporated into the ink-receiving layer are zeolite, precipitated calcium carbonate, ground calcium carbonate, magnesium carbonate, kaolin, talc, calcium sulfate, barium sulfate, titanium oxide, zinc oxide, zinc sulfide, zinc carbonate, satin white, aluminum silicate, diatomaceous earth, calcium silicate, magnesium silicate, amorphous silica, aluminum hydroxide, alumina, alumina hydrate, aluminosilicate, lithopone and urea-formalin resin filler. These pigments may be used alone or in any combination of at least two of them.
Preferably used herein are amorphous silica, alumina and alumina hydrate among others, because of their excellent ink-absorbing capacity.
The amount of these pigments to be incorporated into the ink-receiving layer ranges from about 20 to 90% by weight and preferably 30 to 80% by weight on the basis of the total weight of the solid contents of the ink-receiving layer. In this respect, if the amount of the pigment exceeds 90% by weight, the resulting ink-receiving layer may have reduced film strength, while if the amount thereof is less than 20% by weight, the resulting ink-receiving layer may have a reduced ink-absorbing capacity and insufficient ink-drying properties after recording and the quality of images may correspondingly be impaired.
Moreover, in the present invention, it is also possible to simultaneously use a polymer, which shows cationic characteristics through dissociation when dissolved or emulsified in water, as a cationic polymer component. Examples of such cationic polymers are poly (diallyldimethylammonium chloride), diallyldimethylammonium chloride-acrylamide copolymer, diallyldimethylammonium chloride-sulfur dioxide copolymer, poly (allylamine) hydrochloride, allylamine hydrochloride-diallylamine hydrochloride copolymer, N-vinyl acrylamidine hydrochloride-acrylamide copolymer, dialkylamine-epichlorohydrin addition polymer, polyamide polyamine epichlorohydrin polymerized product, dicyandiamide-formalin polycondensate, polyethylene polyamine-dicyandiamide polycondensate, poly (ethyleneimine) hydrochloride, poly (meth) acryloyloxyalkyl dialkylamine hydrochloride, (meth) acryloyloxyalkyl dialkylamine hydrochloride-acrylamide copolymer, poly (meth) acryloyloxyalkyl trialkylammonium chloride, (meth) acryloyloxyalkyl trialkylammonium chloride-acrylamide copolymer, poly (meth) acrylamide alkyldialkylamine hydrochloride, (meth) acrylamide alkyldialkylamine hydrochloride-acrylamide copolymer, poly (meth) acrylamide alkyl trialkylammonium chloride and (meth) acrylamide alkyl trialkylammonium chloride-acrylamide copolymer.
The ink-receiving layer further comprises, as an adhesive, for instance, aqueous adhesives such as starch derivatives such as oxidized starch and etherified starch; cellulose derivatives such as carboxymethyl cellulose and hydroxyethyl cellulose; casein, gelatin, soybean protein, completely (or partially) saponified polyvinyl alcohol, silanol-modified polyvinyl alcohol, acetoacetyl group-modified polyvinyl alcohol, salts of styrene-maleic anhydride copolymer, styrene-butadiene type latexes, acryl type latexes, polyester polyurethane type latexes and vinyl acetate type latexes; or organic solvent-soluble resins such as poly (methyl methacrylate), polyurethane resins, unsaturated polyester resins, vinyl chloride-vinyl acetate copolymer, polyvinyl butyral and alkyd resins. These adhesives may be used alone or in any combination.
These adhesives are in general used in an amount ranging from about 1 to 200 parts by weight and preferably about 10 to 100 parts by weight per 100 parts by weight of the pigment.
Further, the ink-receiving layer may additionally comprise other additives such as a pigment dispersant, a thickening agent, a cross-linking agent, a fluidity-improving agent, an anti-foaming agent, a foam-inhibitor, a releasing agent, a foaming agent, a penetrating agent, a coloring dye, a coloring pigment, a fluorescent brightener, an antiseptic agent, an anti-fungus agent and/or a water resistance-imparting agent, in an appropriate amount.
The ink-receiving layer can be prepared by applying a coating liquid for forming ink-receiving layers onto at least one side of a substrate using a coating means such as a bar coater, a blade coater, an air-knife coater, a gravure coater, a die coater or a curtain coater, in a coated amount, as determined after drying, ranging from about 2 to 30 g/m2 and then drying the coated layer. This is because if the coated amount is less than 2 g/m2, the quality of the resulting image may be impaired, while if it exceeds 30 g/m2, the resulting sheet may have reduced film strength.
After the formation of the ink-receiving layer, the ink jet-recording sheet may be passed through a roll nip under pressure using, for instance, a super calendar or a gloss-calendar to thus impart surface smoothness to the layer in order to, for instance, make the layer highly glossy.
A glossy layer may further be applied onto the foregoing ink-receiving layer. This glossy layer may principally comprise a resin. Moreover, the glossy layer may likewise comprise a pigment in addition to the resin. The glossy layer is preferably porous or permeable to liquids insofar as the glossiness is never impaired so that ink may rapidly pass through the layer or may be absorbed by the same. To this end, it is desirable to incorporate a pigment into the layer or to select such drying conditions that the resin is not completely converted into a film and that the glossiness is not impaired.
Pigments used in the glossy layer may be the same as those listed above in connection with the ink-receiving layer, but preferred are, for instance, colloidal silica, amorphous silica, aluminum oxide, aluminosilicate, zeolite and synthetic smectite, because of their excellent glossiness, transparency and ink-absorbing ability. These pigments are desirably included in the glossy layer in an amount ranging from 10 to 80% by weight. The higher the specific surface area of a pigment as determined according to the BET formula, the higher the ink-absorbing ability thereof and therefore, the specific area thereof is preferably not less than 150 m2/g. The average particle size of the pigment preferably ranges from 0.01 to 5 xcexcm and more preferably 0.05 to 1 xcexcm. If using, as a pigment, fine silica particles whose average particle size of the primary particles is not less than 3 nm and not more than 40 nm and whose average particle size of the secondary particles is not less than 10 nm and not more than 500 nm, the resulting product is particularly excellent in the glossiness and printed density. If the glossy layer comprises a pigment as a main component (10 to 80 wt %), the resulting product is particularly excellent in the ink-absorbing ability.
In this case, the glossy layer is excellent in both the ink-absorbing ability and transparency. Therefore, if a cationic compound is incorporated into the glossy layer, a dye for ink is effectively fixed to the glossy layer and the product is liable to be quite excellent in the printed density because of the synergistic effect with the transparency of the glossy layer.
Examples of resins used for forming the glossy layer are water-soluble resins (for instance, polyvinyl alcohols such as polyvinyl alcohol, cation-modified polyvinyl alcohol and silanol-modified polyvinyl alcohol; casein, soybean proteins, synthetic proteins, starches; and cellulose derivatives such as carboxymethyl cellulose and methyl cellulose); water-dispersible resins, for instance, conjugated diene polymer type latexes such as styrene-butadiene copolymer, styrene-acrylates and copolymer methyl methacrylate-butadiene copolymer latexes, vinyl copolymer type latexes such as styrene-vinyl acetate copolymer latexes; aqueous acrylic resins, aqueous polyurethane resins and aqueous polyester resins as well as a variety of resins (adhesives) known and currently used in the field of the coated paper. These resins for forming the glossy layer may be used alone or in any combination of at least two of them.
In this connection, if the glossy layer is mainly formed from a resin, it is particularly preferred to use, as a main component, a polymer or copolymer (hereunder collectively referred to as xe2x80x9cpolymerxe2x80x9d) obtained by polymerizing monomers having ethylenically unsaturated bonds (hereunder referred to as xe2x80x9cethylenic monomerxe2x80x9d). It is also possible to use substituted derivatives of these polymers. Moreover, usable herein also include composites prepared by polymerizing the foregoing ethylenic monomers in the presence of colloidal silica to thus form Si-O-R (wherein R represents a polymer moiety) bonds between these components or those obtained by introducing, in advance, functional groups reactive with colloidal silica such as SiOH groups into the foregoing polymers and then reacting the product with colloidal silica. If such a composite is used, the resulting product is liable to be excellent in the glossiness and ink-absorbing ability.
Moreover, in another embodiment, if using a casting method, the resulting product may be excellent in the ability of releasing from the casting drum. The particle size of the composite particles is not restricted to any particular range, but the particle size, for instance, ranges from about 20 to 200 nm.
In an embodiment in which the glossy layer is formed by a casting method using a heated mirror-finishing drum, the foregoing polymer preferably has a glass transition temperature of not less than 40 and more preferably 50 to 100. If the polymer has a lower glass transition temperature, the film-forming rate during drying is extremely high and the surface porosity of the resulting film is reduced. This may in turn lead to the reduction of the ink-absorbing speed of the glossy layer. In addition, the drying temperature is an important factor. This is because if the drying temperature is too high, the film formation excessively proceeds during the drying step, the surface porosity of the resulting product is lowered and as a result, the ink-absorbing speed is reduced. On the other hand, if the drying temperature is too low, the resulting product has a tendency of reducing its glossiness and the productivity rate thereof is also reduced.
A composition for forming a glossy layer may appropriately comprise a variety of auxiliary agents generally used in the field of the coated paper for printing and ink jet-recording paper for the control of the whiteness, viscosity and flowability and examples thereof are pigments, anti-foaming agents, coloring agents, antistatic agents, antiseptics, dispersants, thickening agents and releasing agents. In addition, a cationic compound such as the foregoing cationic resins may be incorporated into the glossy layer to thus impart an ability of fixing dyes for ink even to the glossy layer. The coated amount of the glossy layer ranges from 0.2 to 30 g/m2 and preferably 1 to 20 g/m2, as expressed in terms of the amount of the solid contents.
In addition, an ink jet-recording sheet having higher surface glossiness may be obtained by, for instance, applying a gloss-developing layer and subjecting the layer to a casting treatment or directly subjecting the ink-receiving layer to a casting treatment. Such a casting treatment can be carried out by, for instance, a wet method, a gelation method and a re-wet method. The wet method comprises the steps of pressing a gloss-developing layer, which layer can be an ink jet-recording layer, applied onto a base paper against a heated mirror-finished drum surface while the gloss-developing layer is still in the wet condition to thus obtain highly glossy finishing. The gelation method comprises the steps of bringing a gloss-developing layer, which layer can be an ink jet-recording layer, applied onto base paper into contact with a gelling agent-containing bath while the gloss-developing layer is still in the wet condition and then pressing the gloss-developing layer in the gelatinized condition against a heated drum surface to thus obtain highly glossy finishing. The re-wet method comprises the steps of once drying a gloss-developing layer, which layer can be an ink jet-recording layer, in the wet condition, again bringing the layer into contact with a wetting liquid and then pressing the layer against a heated drum surface to thus obtain highly glossy finishing.
It is a matter of course that a protective layer may be applied onto the back face of the substrate and/or an intermediate layer may be formed between the substrate and the ink-receiving layer. More specifically, a variety of techniques known in the field of the ink jet-recording sheet production may be used in the present invention.
The term xe2x80x9cliquid inkxe2x80x9d used for recording or printing images is a recording liquid comprising a coloring agent, a liquid medium and other additives. In this connection, the liquid ink includes water based ink, and oil based ink.
Examples of coloring agents for water based ink are various kinds of water-soluble dyes such as direct dyes, acid dyes and reactive dyes.
In addition, examples of such liquid mediums for water-based ink include water or combinations of water and water-soluble organic solvents.
Specific examples of water-soluble organic solvents are monohydric alcohols such as ethyl alcohol and isopropyl alcohol; polyhydric alcohols such as ethylene glycol, diethylene glycol, polyethylene glycol and glycerin; and lower alkyl ethers of polyhydric alcohols such as triethylene glycol monomethyl ether, and triethylene glycol monoethyl ether.
The ink of the present invention may additionally comprise other additives such as a pH adjuster, a sequestering agent, an anti-fungus agent, a viscosity modifier, a surface tension modifier, a surfactant and a rust-proofing agent.
The present invention will hereunder be described in more detail with reference to the following working Examples, but the present invention is not restricted to these specific examples at all. In the following examples, the terms xe2x80x9cpartxe2x80x9d and xe2x80x9c%xe2x80x9d represent xe2x80x9cpart by weightxe2x80x9d and xe2x80x9c% by weightxe2x80x9d respectively, unless otherwise specified.